Disclosure: As an Amazon Associate, PoolUV may earn from qualifying purchases. This article also links to Pool Chemical Calculator resources.
A fresh refill gives a UV and salt pool a clean starting point, but the first few days matter. Tap water usually has little or no stabilizer, salt may be far below the cell target, pH can move quickly, and chlorine demand can spike while the new water warms up and starts collecting debris.
The mistake is adding everything at once and trusting the equipment display. A better start-up sequence rebuilds the basics in order: balance pH and alkalinity, add stabilizer carefully, confirm salt with an independent test, then bring chlorine into range before the salt cell takes over daily maintenance.
Test the fill water before adding salt
Start with pH, total alkalinity, calcium hardness, metals if your source water is known for staining, and temperature. If pH or alkalinity is far off, correct those first so later chlorine and stabilizer adjustments are easier to read. Keep circulation running long enough for each addition to mix before retesting.
Use the Pool Chemical Calculator website or Pool Chemical Calculator app to calculate acid, chlorine, stabilizer, calcium, and salt additions from actual pool volume instead of label estimates.
Add CYA before relying on the salt cell
Fresh water with little stabilizer loses chlorine quickly in direct sun. Add cyanuric acid in stages and aim for the range recommended by your salt system and local conditions. Do not overshoot; lowering CYA usually means replacing water again.
Once stabilizer is dissolving, maintain free chlorine manually with liquid chlorine until the salt cell can hold the target. UV helps treat water that passes through the chamber, but it does not protect chlorine from sunlight in the pool.
Confirm salt after the water is mixed
Salt dissolves fast, but readings can be misleading before the pool has circulated. Brush the floor, run the pump, then verify salinity with a drop test, strip, or digital meter before adjusting the cell setting. If the controller and independent test disagree, trust the independent test first and inspect the cell only after water chemistry is stable.
Add salt in smaller rounds near the target. It is easy to add more, but fixing high salinity usually means dilution.
Inspect UV flow before declaring the start-up finished
After refill, check filter pressure, pump basket, skimmer basket, unions, valves, and return flow. Air leaks or restricted flow can reduce exposure through the UV chamber and make the salt cell report flow or production problems that are really circulation problems.
This is also a good time to inspect the quartz sleeve and salt cell plates. New water will not fix existing scale, staining, or a dirty sleeve.
Keep start-up supplies ready
A refill goes smoother with a complete test kit, salt test, cyanuric acid, liquid chlorine, muriatic acid, pool salt, a brush, and filter-cleaning supplies. Waiting for supplies after the water is already warm and unstabilized is how a clean refill turns cloudy.
Shop salt pool test kits, CYA, chlorine, salt, and pool start-up supplies on Amazon.
FAQ
Should I add salt or stabilizer first after a refill?
Balance pH and alkalinity first, then add stabilizer carefully while preparing salt additions. Keep chlorine in range manually until the salt cell can maintain the pool.
Can I turn the salt cell on as soon as salt is added?
Wait until the salt is fully dissolved and circulated, then confirm the level with an independent test. Turning the cell on too early can create false low-salt or flow confusion.
Does a UV pool need chlorine during refill start-up?
Yes. UV treats water inside the chamber, but the pool still needs free chlorine in the water. Fresh water without enough CYA can lose chlorine quickly in sunlight.
How do I avoid overshooting CYA or salt?
Add both in stages, circulate thoroughly, and retest before adding more. Overshooting either one is much harder to fix than stopping slightly low and adjusting again.